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Concept
Galactose
Summary
Galactose (gəˈlæktoʊs, galacto- + -ose, "milk sugar"), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epimer of glucose. A galactose molecule linked with a glucose molecule forms a lactose molecule.
Galactan is a polymeric form of galactose found in hemicellulose, and forming the core of the galactans, a class of natural polymeric carbohydrates.
D-Galactose is also known as brain sugar since it is a component of glycoproteins (oligosaccharide-protein compounds) found in nerve tissue.
The word galactose was coined by Charles Weissman in the mid-19th century and is derived from Greek γαλακτος, galaktos, (of milk) and the generic chemical suffix for sugars -ose. The etymology is comparable to that of the word lactose in that both contain roots meaning "milk sugar". Lactose is a disaccharide of galactose plus glucose.
Galactose exists in both open-chain and cyclic form. The open-chain form has a carbonyl at the end of the chain.
Four isomers are cyclic, two of them with a pyranose (six-membered) ring, two with a furanose (five-membered) ring. Galactofuranose occurs in bacteria, fungi and protozoa, and is recognized by a putative chordate immune lectin intelectin through its exocyclic 1,2-diol. In the cyclic form there are two anomers, named alpha and beta, since the transition from the open-chain form to the cyclic form involves the creation of a new stereocenter at the site of the open-chain carbonyl.
The IR spectra for galactose shows a broad, strong stretch from roughly wavenumber 2500 cm−1 to wavenumber 3700 cm−1.
The Proton NMR spectra for galactose includes peaks at 4.7 ppm (D2O), 4.15 ppm (–CH2OH), 3.75, 3.61, 3.48 and 3.20 ppm (–CH2 of ring), 2.79–1.90 ppm (–OH).
Galactose is a monosaccharide. When combined with glucose (another monosaccharide) through a condensation reaction, the result is a disaccharide called lactose. The hydrolysis of lactose to glucose and galactose is catalyzed by the enzymes lactase and β-galactosidase.
Official source
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